Income Per Share of Common Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Income for basic and diluted income per common share (in dollars)	$ 4,626	$ 4,060	$ 7,382	$ 8,684
Denominator:
Weighted-average shares for basic income per share	5,560,000	5,550,000	5,559,000	5,861,000
Effect of dilutive securities:
Employee and director stock options (in shares)	9,000	9,000	9,000	12,000
Adjusted weighted-average shares and assumed exercises for diluted income per share	5,569,000	5,559,000	5,568,000	5,873,000
Income per share of common stock:
Basic (in dollars per share)	$ 0.83	$ 0.73	$ 1.33	$ 1.48
Diluted (in dollars per share)	$ 0.83	$ 0.73	$ 1.33	$ 1.48
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	9,900	10,000	9,900	10,000